The ability of a pneumatic tire to run when it is entirely deflated, while always an important factor, has become an increasingly important factor in the design of pneumatic tires. A great deal of emphasis is now being focused upon this characteristic of the tire due to the effort to conserve our scarce raw materials, the effort to eliminate the spare tire in an automobile and the effort to provide a stable, safe tire construction which can withstand the rigors of being run uninflated for at least a certain distance at a certain minimum speed without destroying the remaining useful life of the tire.
The present construction represents an improvement in the design of a pneumatic tire to facilitate its run-flat characteristics. The present construction yields a stable, easily controlled tire when it is run uninflated. This feature adds to the safety of the vehicle operator if it is necessary to run on a deflated tire.
This construction prevents the bead from unseating when the tire is run flat. This construction protects the tire from being damaged during its run-flat operation and helps to preserve the remaining useful life of the tire. If the bead is unseated during the time the tire is being run flat, the bead will drop into the drop center portion of the rim. In this condition, the tire is very unstable and difficult to drive and the tire will be easily damaged by the rim flange cutting into the sidewall.
The prior art has attempted to maintain the bead seated on the tire by other methods; for example, by providing the rim with radially outwardly projections (called safety humps) located axially inwardly of the tire bead so that the tire bead is trapped between these projections and the rim flange. Safety humps, although meeting with some success, have drawbacks which this invention overcomes. When run-flat, the bead is forced upward and away from the rim. The safety humps, to be effective, have to be very high and thus provide difficulty in mounting. Also, the safety humps require another operation in the manufacture of the rim.
Another method is to physically trap the beads between a member which extends axially from the inside of one bead to the inside of the other, bridging the gap between the beads. These members are expensive, complicated and provide difficulty in mounting and dismounting the tire. They have proven to be generally unfit and have had little, if any, commercial application.
Protrusions located in the lower sidewall area of the tire have been proposed which are designed to rest upon the rim flange, but these protrusions have had the drawback that they would not prevent the tire bead from becoming unseated during operation in a run-flat condition. The novel construction of this invention departs from these prior disclosures in the following manner:
1. A substantial portion of the bead latch is located axially outwardly of the rim flange. A part of this portion extends beyond the rim flange both axially outwardly and radially inwardly of the rim flange so that this portion may engulf the rim flange when the tire is run flat. PA1 2. The diameter of the radially inwardly extending portion of the bead latch is less than the outer diameter of the rim flange. PA1 3. A portion of the recessed portion of the bead latch is not in contact with a portion of the rim flange when the tire is in its inflated condition without bearing a load. PA1 4. The rim flange is completely engulfed by the bead latch in the footprint area of the tire when the tire is inflated and under load with part of the bead latch located on the radially inner side of the rim flange.
The novel construction of this invention provides a bead latch which is located in the lower sidewall area of the tire radially outwardly or above the position of the rim flange when the tire is placed on the rim. A substantial portion of the bead latch extends axially outwardly beyond the rim flange for a substantial distance and a portion of this axially outwardly extending part of the bead latch extends radially inwardly of the rim flange. This results in the outer diameter of the rim flange being greater than the diameter of the bead latch.
Due to the compression which the bead has against the rim flange, the novel construction of this invention does not contact the rim flange throughout the entirety of the rim flange, as do the prior art protrusions. This factor results in easily mounting and dismounting of the tire containing the bead latch, a decrease in the abrasive wear which the bead latch would encounter when engaged to the rim flange and in the bead latch being somewhat inoperative during the normal operations of the tire.
It is an object of this invention to provide a tire construction which will prevent the bead from unseating from the rim flange when the tire is run flat thereby preventing the tire bead from dropping into the drop center portion of the rim.
It is another object of this invention to provide a tire construction which will be stable when being operated in a run-flat condition.
It is a further object of this invention to provide a tire which will be capable of being run flat without damaging the remaining useful life of the tire.
other objects will be evident from the detailed description of this construction which follows: